The present disclosure relates generally to radome films and, more particularly, to low permeable materials for radome films.
A radome is an enclosure that protects a device, such as a microwave or radar antenna. The radome is constructed of material that minimally attenuates electromagnetic signals. Radomes also serve to protect antenna surfaces from weather or to conceal antenna electronic equipment from view. Radomes can be spherical, geodesic, planar, etc., depending upon the particular application and may be ground or aircraft based.
Slip cast fused silica (SCFS) is a porous material that is commonly used in radomes that are required to have low loss characteristics with respect to various types of microwave energy, to withstand broad temperature excursions and to survive extreme physical stress. The migration of electronics to non-hermetic packaging, which is housed within the radome, has thus exposed certain sensitive devices to environments to which the radome likewise is exposed. Of particular concern is exposure of the electronics to moisture where the porosity of the fused silica allows both liquid and vapor to pass through. The low coefficient of thermal expansion (CTE) of the fused silica also presents challenges to attempts to infiltrate or coat radome systems to thereby reduce liquid or vapor transmission.
Indeed, previous attempts to address the problems of SCFS have involved remelting the surface of the SCFS to form a continuous “glass” layer. This process tended to ultimately compromise structural requirements of the assembly or resulted in cracks that allowed rapid influx of water vapor. Vacuum infiltration of SCFS with a liquid silicone material has also been attempted. Here, the silicone material prevents liquids from passing through the radome wall but does not limit its water vapor transmission rate (WVTR). Desiccants have also been used inside the radome to lower moisture levels but this is an “after-the-fact” solution that does not prevent moisture infiltration.